Generally in the processes for preparing IC or LSI, wafer baskets for encasing therein a large number of flat silicon wafers and conveying them are widely used. On the wafer baskets, a discrimination mark indicating a production lot number, a production date, etc. is provided at the request of the process control, and the silicon wafers encased in each wafer basket are individually controlled by reading the discrimination mark.
Accordingly, there have heretofore been proposed wafer baskets of various types, for example, a wafer basket wherein a recording device is provided in the basket body and information is read out by means of the recording device through a display element such as a crystal element as described in Japanese Patent Laid-Open Publication No. 236136/1986, a wafer basket having a ceramic resonance means embedded in the basket body as described in Japanese Patent Laid-Open Publication No. 267338/1986, and a wafer basket having an IC card molded together with the basket body as described in Japanese patent Laid-Open Publication No. 123735/1987.
In those conventional wafer baskets, however, various supplementary equipment is required, and hence it is thought that not only the cost therefor increases, but also the production of those baskets becomes rather difficult because of a restriction of temperatures, etc.
On that account, the present applicant has proposed a basket of another type in Japanese Utility Model Application No. 25889/1990. This basket has a structure such that a mark plate provided with a discrimination mark such as a bar code is fusion bonded onto an outer peripheral surface of the basket body. This basket can be prepared relatively easily and the information for the production control can be easily read out without providing any expensive supplementary equipment.
The basket described in the above Japanese Utility Model Application No. 25889/1990 has the desired effects. However, it has been found that a thermal strain of the basket body is sometimes caused by the heat applied when the mark plate is fusion bonded to the basket body. If the heating time is shortened to prevent occurrence of such heat strain, the depth of the fused portion is made shallow to thereby to lower the bonding strength, resulting in incomplete bonding between the mark plate and the basket body.